Electrolyte



July 3, 192s.

zofzxm ou m w 5 Patented July 3, 1928.

j :UNITED STATE-s, PATENT OFFICE.

HUMPHBEYS o. sIEeMUND, or wEsroxANeE, Naw JERSEY, AssxGNoa To ELECTRIC COMPANY,

NEW YORK.

INcoBrOaa'ranOr NEW Yonx, N; Y., A CORPORATION o! masseuse i j Appntatim:neapecuniaria),1924.v serial No. 758,574.

This invention relates 'to elec-trol tes for e electrolytic 'cells and to methods i or prof ducing the same. It has particular reference to electrolytes for use in electrolytio i condensers, such as are employed in ltelephone power plant installations, forexample, though it is not limited to thisclass of electrolytic condensers alone.

As is well. known,'a dielectric .film isv l formed on the surfaces ofz film-forming metals such as aluminum, when they arehem-r' ployed as anodes in an electrolyte. rllhis lm gradually 'builds up to a thickness coi'-V responding to the voltageimpressed,*thereby retarding the flow of current from thel anode to the electrolyte. `The combination of this film with the electrode and elec` trolyte forms a condenser when thecurrentflow is such as to make the film-forming l electrode an anode.

Some of the more common electrolytesV which are employed in electrolytic condensf,

ers are borates and boric acid, tartrates and tartaric acid, citrates and citric acidv and phosphates with phosphoric acid. This invention has particular reference to electrolytes4 comprising ammonium hydroxide, .boric acid andwater, though it will be appreciated that certain features ofthe in"- vention are not limited to this class of elec-p trolytes alone. ,v

`lt.is an object of the invention to provide an elcctrolytic condenser electrolyte which possesses a long life and which will produce a condenser of suitably low impedance.

v A further object of the invention is a simple and efficient method of producing such electrolytes.

A. i'eature'of the invention is the production of av group of ammonium hydroxideboric acid-electrolytes that have definite hv-V drogen .ionconcentration values and specific resistance values.

The impedance of this condenser is equal tothe squareroot of the sum of' the. squares of the reactanc'e and the4 In accordance with 'the'invention therel have' been worked out -certain relations from' which the proper proportionsofammonim hydroxide, boric acid andv water'ma be de# terminedto produceelectrolytes-having deli#- nite specific resistance centration values,` y u v When used across clrcujits of compara-V tively low potential, suchfas'in'telephone exi andhydrogen ion .coni change power plant installations'where=the` electrolytic condenser is applied acroslsfcire' cuits of comparatively low, unidirectional,

pulsating potential, it hasl been found that.-` the leakage current does not' form an especially` important factor inthe choicevv of the" electrolyte, so long` as itsl value is" reason? ably' low; a leakage'current of 4 or''micro-` amperes perl squareJ inch, for instance, has@ been found permissible. "Y Onzthe otherlhand,

low impedance of c ondensersfand long life ofy electrolytes have vbeenlfoun'd to be cially desirable in such"'cndens'ers. l

The single figure of the Vdrawing shows a SPe" graphical representation of the jrelatiorrbe-v tween the proportions of. the components and the specific resistance and hydrogen'ion concentration PH values ofv ,electrol tes comprisingv ammonium hydroxide boric acid (HBBOS) and water. l y

A` fuller understanding of thein'ventionv will be had from the' more detailed description Vto follow. i i

In accordance with a feature of the invention there is provided a group of'el'ec! trolytes comprising ammonium hydroxide,

boric acid and water having specific resist-V ance values between 150 and 800 ohms per cubic centimeter and hydrogen. ion concentration values between y6.8 and 7.8. Such electrolytes have been found to comprise between 250 and 900 grams of boric acid and between 20 and 125 Cubic centimeters of a 28.5% ammonium hydroxide solution dissolved in 19 liters, A(5 gallons) of water. These electrolytes have been found to be satisfactorily llong lived and to' form low impedance condensers,which characteristics are e -condensers comprising, for example, an insulatingcasing, a cover for the casing, an aluminumdor other film formmg materlal roo anode,`and suitable cathodes suspended from, and attached-to terminalsin, the cover may be employed with the electrolytes of the inv vention. ,The electrolytes of the invention are' introduced into the casing, the electrodes being immersed in them.

It has been found that electrolytes which are appreciabl-y alkaline dissolve the filmforming electrode more readily and rapidly than neutral electrolytes and are therefore short-lived -due to the contamination of the electrolytes by the dissolved metal. Appreciably alkaline electrolytes Vhave also been found to be undesirable in that their use re'- sults in excessively high leakage `Zcurren'tsf particularly .at elevated temperatures. Alkaline electrolytes were found, howeVer,- to possess -theadvantage of not appreciably 1nciting corrosion onfthe surface of the filmsistance, the hydrogen ion concentration,

,Acid lelectr lyt'es forming electrodes; 1

Acid electrolytes, such as solutions saturated with boric acid and containlng' only a relativelyY small quantity of ammonia hydroxide, weretfound to incite Acorrosion on the hlm-forming electrode; .The hydrogen ion concentration of' acid'V electrolytes was also found to besubstantially unstable Wlth changes influid concentration, thereby making such, electrolytes -further undesirable.

to produce thickv lmson the film-forming electrode, thereby causing low leakagecurrents; this fact tends'to'make acid electrolytes desirablein thosel cases in which the likelihood of corrosion occurring is ofpminor consideration. *As minimum leakage cur-v rents are not particularly important .in condensers for use insuch Ycircuits as those eny countered in telephone power plant installations while the life of electrolytes :and electrodes 'is an especially important factor in' such cases, acid electrolytes should be avoided in such use of electrolytic condensers.

For the production of electrolytes havmg long life and producing low impedance condensers, a solution must be of given reslstance and a balance must be reached between that.,

and the composition, of various electrolytes;

these curves were produced by determining'-AV these points on the curves A B C D E, which have, however,- been found...

represent ,the compositions f having-certaing definite' 'hydrogen "ion .concentration` values#v and then .drawing e. the individual curves substantially'netral (those having Pg/Values sented by the curve H; solutions which are acid (those having PH values less than 7)v v .arerepresented by the curves to the right o! curve H, this range of curves being there termed the `alkaline range; The curves M N -O represent the relation between the individualcharacteristics of electrolytes having constant proportions ofl boric acid and ammonia, the boric-acid-ammonia ratioswhich are represented by the individual curves being shown attherright of the drawing.

'Referring to the ligure'of the drawing, the speciic resistance'and strength of acidlty or alkalinity '('hydrogen ion concentrationidesignatedby' PH) 'of various electrolytes composed 'of ammonium hydroxide, boric acid andV water are shown byI the through thesepoints,t Solutions which are* fr p W y '70;,1 substantially equal to '7) are those repre-QT fore -termed the acid.Y range; alkaline solu tions (those vhaving APH values greater than 7) are represented by the curves'totheleft of curve I-I,V thisk rangeof curves being curves. In accordance with 4these curves, it

has beenfound that for acid' or lslightly alkaline solutions'the specific resistance of a particular electrolyte is fixed by the ammonium hydroxide yc-ontent and is practically independent off the boric acid content; and, further, that the proportions of boric acid and ammonium hydroxide to form neutral solutions lvary .with the' degree of dilution by water. c 1

Asa result of the former. of these characteristics, electrolytes having any desired value. of specific resistance maybe formed by mlxing varying quantities of boric acid, ammonum hydroxide and water while maintaining the ratio of'ammonium hydroxide to Water constant. For example, an electrolyte having a specific resistance of 350 ohms per cubic. centimeter may be forme-dby mixing 300 grams of boric acid with 19 liters of water and 50 .cubic centimeters of 28.5%,

ammonium hydroxide, or by mixing'lQOO grams of boric acid withfthe sameamounts of water and .Lammonium hydroxide. In this mannen, electrolytes having specific resistances which are constant and hydrogen ion concentration Avalues varying` from ap- Vpreciably alkaline4 to appreciably acid can be produced.

v.The .latter .of evident by comparing the curves F G I-I,

representing the characteristics of electro-.- lytes having definite PH. values', y withA the Y these` lresults will 'be I more i curves `M N O, which represent the charac-4.

teristics of' electrolytes having constant proportions of boric acid: andammonium-hy-V droxide. A.The curves M ,N O,1it will be noted, cross the'curves of constantl hydrogen ion concentration-F. G H and asa result of these intersections it followstliat; tlieliy-v l drogenv ion concentration o fa s olution con tainiiiggiven amounts of boric acid4 and a1n monium hydroxide: will depend upon"l the boi-'ate solutions may be. appreciably changed bythe addition of lwater or. if desired, a oid electrolytes may be neutralized..oriiiade alkaline bythe addition ofl an amountfof water which will produce vaY solution of the concentration which corresponds Von the curve to Vthe hydrogen ion concentration value desired. Solutions whose hydrogen ion concentration value is approximately equal to 8, are not, however, appreciably changed as regards their hydrogen ion concentration by the addition `of water. Solu- .tions .having .hydrogen ion concentration values which are equal and which are less than 8,.,buthaving differentspecific resi-stv ances will therefore, comprise differentpro-j .portions ofboric acid andammonium hy;

droxide .Electrolytes eomprisingboric acid. ammonium hydroxide and water which are nearly neutral and slightly alkaline and produce low impedanceoondensers have been foundl to comprise the. band of electrodes represented by the shaded regionin the drawing.' This band of electrolytes comprises those obtained by mixing ammonium hvdroxide, boric acid and water on the basis ofa hydrogen ion v conce-ntrationvalue .-iixed between the limits of 6.8 and 7.8. While all electro'- lytes` lying in this band have been found satisfactory, the preferred-series of electrolytes comprises those between pH:y 7 .5 andl -pH=7.2, and above` the 150 ohm per cubic centimeter resistance.lin`e. V

The proportions of ammonium hydroxide boi-*ie-acid-andwater which may be employedinmaking up these preferred electrolytesyare `sziven in the following 'table in.

accordance Withtheeurves ofthe invention.

' Table giy`es' .the cliaraeteristics of iarious electrolytes whose vcoinpo'sitionsare expressed in terms of a watercontent of -5"gallons,

vwhile Table II givesthe characteristics of the same electrolytes having their. co1nposi tions expressed in terms' o'f-.a water content.

of one liter." e

The proportions of anii'noniiini' hydroxide, boi-ic acid and water which may b'e'emp'loyed niay be considerably varied,zcha`nges in such proportions .varying the speciticjresistanee' and hydrogen ion lconcentration .of theparh ticular Aelectrolyte formed. 'As a'general rule, the specific resistance `.l`ia'sbeen found to depend i uponjandincrease with 'the 1,iatio, weightv of watei'f; weight' of aninionia`(N H3)', while the hydrogeiiion concentration value has been found tobe-dependentifupon the ra tio, weight of ammonia: Weightof borie acid (HaBO), and 'the degree of .dilution by water. By actual test, it has been foundthat the electrolytes contained' in 'tl'ieband shaded in the drawing possess long life forni condensers having iiiipedances which are pai vticlilarly well adapted .fortise in suoli. cir'- euits as are encountered in telephone power plant installations, for example. A"Vliile prefel-red proportions 'have'been'stated herein, Y

fit will be understood, however` that it is n ot intended to impose' anyrestrictions upon the proportions'oth'er than those set forth in the claims.

The range in temperatures which may be employed with the electrolytes of the invention is dependent primarily upon thecompositioii of .the particular electrolyte employed, any one electrolyte being substantially limited to` use at a'teinperature notappreciably lower V.than the saturation temperature of .said electrolyte. The usual room temperatures have ,been found to be substantially :above the lowerlimit as defined above.

-zThei voltages which may be satisfactorily employedA with lthe electrolytes of the invention may beeonsiderablyvaried, actual practice having` shown that eondensers containing these eleetrolytesmay be satisfactorily applied across circuits of from 2 to 300 volts potential, at least.

Any suitable film-formingr electrolyte may be used to replace. ammonium berate solutions solang as theparticular electrolyte employed possesses. specific resistance and hydrogen ion concentration values lying 1n the regions defined in the descriptlon of the .curves referring to boric acid.

The impedance ofthe electrolyte in a given condenser is governed not only by the specific resistance of the electrolyte but also by the specific construction of the condenser, the applied voltage and operating temperature. The factors ot design which determine this resistance are the distance between and the area of the plates of the condenser.

For example, the resistance of thel electrolyte will vary directly with the thickness of the electrolyte (distance between the plates) and .inversely withk the cross-section ofthe electrolyte (areav of the plates). A

The concentration ot' ammonium hydroxide as employed herein is intended to define the percentage by weight of ammonia.v (NH3) prises a mixture of a solution of an acid, a

solution of a base, and water in such proportions'that said mixture posseses a specific resistance value between 150 and 800 Ohmsper cubic centimeter vand a hydrogen ion con-v centration value between 6.8 and 7 .8.

2. A iilm forming electrolyte which comf-prises a mixture of boric acid,'ammonium` hydroxide and water in such proportions that said mixture possesses a hydrogenioii concentration value between 6.8,and 7.8 and a specific resistance valuebetween 150 and 800 ohms per cubic centimeter.-

3. A film forming electrolyte which comprises a mixture of. an acid, ammonium hydroxide, and water, the ratio ot the volume of water in cubic cent-imeters to the volume of '28.5% ammonium hydroxide 'being as great as 152 and the ratio of the amount ol water to t-he amount of acid being such that the electrolyte is Ysubstantially neutral.

4. A film forming electrolyte which kcomprises a mixture of boric acid, ammonium hydroxide yand water, the ratio ofthe volume of water in cubic .centimeters to the' volume ot 28.5% ammonium hydroxidei-n .cubic centimeters being as small as 19.50 andthe ratio of the volume'ot water 'tor the weight ofboric acid being such that the electrolyte possesses a hydrogen ion concentration value Vbetween 6.8 and 7.8.

5,'A film forming electrolyte which comprises the-I- following substances in subst-antially the following proportions, water 19 liters, 28.5 ammonium hydroxideQO to 125 cubic'centimeters, boric acid 250 to 900 grams, the hydrogen ion concentration of" said electrolyte being' between 6.8 and'7.8.

6. Alilm forming electrolyte Vwhich comprises substantially 250 to 900 grams of boric acid and ammonium 'hydroxide dissolved in 19 liters of water, the amount of vammonium hydroxide being at least small enough to produce a high specific resistance, and a hydrogen'ion concentration between 6,8 and 7.8i .7. A iilm forming electrolyte which comprises" substantiallyl 250' tov 900 grams of boric acid and ammonium hydroxide dissolved, in 19 liters ot'- water, the amount of ammonium hydroxide being at least small 'cnough'to produce a 4specific resistance-be-A tween 150 and 800 oliins'pcr cubic centimeter, vand a-` hydrogen 'lon concentration between 6.8 and'7.8.

8. A film forming electrolyte which comprises substantially 20 to 125 cubic centime- Y 'ters ot' 281/270 ammonium hydroxide and' boric acid in 19 liters of water,'the amount ot' boric acid being sufficient to produce a substantially vneutral solution.

9. A lilm forming electrolyte which comprises'substantially 20 to 12,5 cubicc-entimeters of 28%70' ammonium hydroxide and 'boric acid in' 19 liters ot water." the amount4 of boric acid being sufficient to produce a hydrogen ion concentration value between 6.8 and 7.8.

10. A film formi-ng electrolyte which comprises 28V2% ammonium Vhydroxide and boric acid dissolved in 19 liters of water, the ratio of the weight in grams of boric acid to the volume in cubiccentimet'e'rs of ammonium hydroxide being between 6.6- and 16.5, and the hydrogen ion concentrationbeing` between 6.8 and 7.8. v Y

1l. A tilmfto'rming electrolyte comprising boric acid, ammonium hydroxide and water in such'proportions'as to possess a specific resistance between 150 and 800 ohms per cubic centimeter and a hydrogen ion concentration Vahle between 7 .2 'and 7.5.

In witness whereof, I hereunto subscribe my name this 26th'day of December, A. D. '1924.

HUMPHREYS o. snaGMUND. 

